Field of the Invention
The present invention relates to wireless communications, and more specifically, to a method and apparatus for transmitting an indication in a wireless communication system.
Related Art
Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). A long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
Carrier aggregation (CA) may be introduced. In CA, two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. A Rel-10 UE with reception and/or transmission capabilities for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells. A Rel-8/9 UE can receive on a single CC and transmit on a single CC corresponding to one serving cell only.
When CA is configured, a user equipment (UE) only has one radio resource control (RRC) connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the non-access stratum (NAS) mobility information (e.g., tracking area identity (TAI)), and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as the primary cell (PCell). In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (DL PCC) while in the uplink it is the uplink primary component carrier (UL PCC).
Small cells using low power nodes are considered promising to cope with mobile traffic explosion, especially for hotspot deployments in indoor and outdoor scenarios. A low-power node generally means a node whose transmission (Tx) power is lower than macro node and base station (BS) classes, for example a pico and femto eNodeB (eNB) are both applicable. Small cell enhancements for the 3GPP LTE will focus on additional functionalities for enhanced performance in hotspot areas for indoor and outdoor using low power nodes.
For one feature of small cell enhancements, dual connectivity may be introduced. Dual connectivity is an operation where a given user equipment (UE) consumes radio resources provided by at least two different network points (master eNB (MeNB) and secondary eNBs (SeNBs)) connected with non-ideal backhaul while in an radio resource control (RRC) connected state (RRC_CONNECTED). Furthermore, each eNB involved in dual connectivity for a UE may assume different roles. Those roles do not necessarily depend on the eNB's power class and may vary among UEs.
When a UE has dual connectivity with a macro cell and small cells, a method for configuring a SCell efficiently may be required.